Mithra is the antagonist of Moonlight Syndrome and by extension the Twilight Syndrome games as well, causing the titular syndromes. Although he appears as a young child, Mithra is very violent, manipulative and cruel, killing Yukari Hasegawa, Arisa Kahara, Chisato Itsushima and Mika Kishi. He is killed by Ryo Kazan, who wields a katana to tear him apart in the conclusion of the story, apparently bringing an end to the syndrome.
Mithra also appears in a single scene in killer7 in the Alter Ego chapter, referred to as "The Oracle" in Hand in killer7. His reason for being there is unknown, though it may be connected to the full moon appearing at the beginning of each mission. As The Oracle, he appears as twins who have the voice of an old man.
Mithra is the Zoroastrian god of contract, a real figure in Zoroastrian mythology. However, in Zoroastrianism Mithra is an exalted and benevolent figure, while in Moonlight Syndrome he is a ruthless villain and in killer7 he is mysterious and represents duality.